Shell-lattice metamaterials with intrinsic contact stabilization for exceptional mechanical performance and nonlinear stability

Although lattice mechanical metamaterials offer low weight and tailorable properties, they face a fundamental barrier to adoption at low relative densities: optimising elastic-plastic performance usually results in reduced buckling resistance (nonlinear stability). Here, we present a novel shell-lattice metamaterial design methodology that eliminates the need to compromise between high yield strength and nonlinear stability at low relative densities. This methodology also provides high specific stiffness and high energy absorption. Our design features seamlessly integrated elliptical hollow struts and hollow spherical nodes. Leveraging a stretching-dominated mechanism augmented by contact-enhanced stabilisation, the architecture provides compensatory reinforcement under large deformations. We numerically investigate and experimentally validate the influence of key geometrical ratios on the mechanical properties. Crucially, elastic isotropy can be achieved through parameter optimisation, and broad tenability enables customised anisotropic elastic responses for diverse applications. Across relative densities ranging from 0.01 to 0.5, our proposed shell lattices demonstrate consistent superiority over conventional truss and shell lattices of equal density. At a relative density of 0.1, the designs deliver a 5 % rise in Young's modulus, a 38 % increase in yield strength, and almost double the energy absorption capacity, significantly outperforming conventional TPMS-like shell lattices. These enhancements arise from internal contact mechanisms that stabilise post-buckling behaviour, yielding consistent or enhanced stress-strain responses. This methodology overcomes the limitations of low-density stretching-dominated lattices, paving the way for advanced, lightweight, load-bearing structures, energy absorbers, and multifunctional metamaterials.